1. Field of the Invention
This invention relates to communication systems. In particular, the invention relates to frequency planning and bandwidth allocation in a communication system.
2. Description of Related Art
In a typical communication system, a number of users are allocated bandwidths in a frequency band for signal transmission and reception. A transponder, such as a satellite, receives signals transmitted from transmitter communication units (CU""s) and re-transmits the received signals to receiver CU""s. A communication system may include a number of transponders, each operating at a different frequency band.
There are a number of performance requirements involving the allocation of user bandwidths. First, the allocation should be efficient, i.e., the allocation preferably supports as many users as possible without wasting bandwidth. Second, the allocation should be such that adjacent channel interference (ACI) is minimized as much as possible to reduce noise affecting signal quality. Third, the allocation should be able to accommodate a dynamic environment when users are added or removed in the system. Fourth, each CU should be able to process data as fast as possible without incurring costs. Currently, there is no system that can achieve all of the above requirements.
In a typical communication system that involves a large number of users, the frequency allocation or planning is performed in advance and each user is assigned a predetermined bandwidth. To avoid channel fading and to increase data security, the user operating frequencies are changed periodically. A well-known technique to do this is the frequency hopping method.
In the frequency hopping technique, the user frequencies are hopped at a randomly generated hop frequency at predetermined time intervals. To avoid interference, each user CU calculates its hop frequency such that the resulting new frequency is different from other users. This calculation requires each user CU to consider all the other user frequencies. The data storage and processing time for each CU are therefore extensive, resulting in degraded performance and expensive CU design.
Therefore there is a need in the technology to provide frequency allocation and planning to achieve the above performance requirements in a frequency hopping communication system.
The present invention is a method and apparatus for providing orthogonal frequency hopping for users in a communication system. The users have user bandwidths allocated on a frequency band. A jitter space is provided with a jitter bandwidth on the allocated frequency band. If at least one of the user bandwidths is larger than the jitter space, a skip zone is determined for at least one of the user bandwidths. The skip zone is unoccupied by a starting hop of the user bandwidths when the user bandwidths are shifted in a frequency hopping.
In a preferred embodiment, a communication unit provides an operational frequency in the frequency band. The communication unit includes a random generator, a network implementation plan (NIP) parameter storage, and a frequency generator. The random generator provides a random index when a frequency hopping occurs. The NIP parameter storage provides orthogonal frequency hopping (OFH) parameters. The frequency generator is coupled to the random generator to generate the operational frequency based on the random index. The operational frequency is orthogonal to other user frequencies in the frequency band.